Metallocene compounds such as bis(cyclopentadienyl)titanium dialkyl or bis(cyclopentadienyl)zirconium dialkyl in combination with aluminium alkyls are well known homogeneous olefin polymerization catalysts. DE-2,608,863 describes the use of bis(cyclopentadienyl) titanium dialkyl in combination with trialkylaluminium and a controlled amount of water.
The controlled hydrolysis of aluminium alkyls gives rise to the formation of species containing an Al--O bond (aluminoxane) which are effective co-catalysts of metallocenes. Kaminski (Adv. Organomet. Chem. 18, 99, 1980) disclosed that aluminoxanes in combination with dichlorometallocenes produce catalytic systems very active in ethylene polymerization.
However, it is also possible (Turner, EP 277004 and Ewen et al. EP 426637) the use of co-catalysts based on bulky boron compounds which, acting as non-coordinative anions, stabilize the cationic metallocene without preventing the incorporation of the olefin in the polymerization process.
The most olefin polymerization processes make use of homogeneous catalytic systems. This results in very high activities. However industrial processes require heterogenous systems which on one hand produce polymers having controlled morphology, on the other hand maintain the activity of homogeneous systems.
EP 206794 discloses heterogeneous catalysts obtained by simultaneous or subsequent (in any order) addition of aluminoxane and metallocene onto an inorganic support.
This process, according to EP 260130, is also applicable to multicomponent systems, that is catalysts containing either several metallocenes or a metallocene and a non-metallocene transitional metal compound. In this way polyolefins having multimodal molecular weight distribution are obtained.
EP 361866, EP 323716, EP 367503, EP 368644 and U.S. Pat. No. 5,057,475 describe the preparation of a heterogeneous catalytic system composed by an aluminoxane and a metallocene characterized in that the aluminoxane is generated in situ by reaction of a trialkylaluminium with undehydrated silica. The use thereof in O-olefin polymerization results in high activities.
Another well known technique used in the preparation of heterogeneous catalysts is chemical modification of the inorganic support. EP 474391 and EP 314797 disclose a process wherein the support, before addition of the metallocene, is treated with an organoaluminium compound which reacts with the hydroxy groups present on the silica surface.
The above described methods produce heterogeneous catalysts which present the drawback that the catalyst is not tightly bonded to the support so that separation of the metallocene from the inorganic support occurs.
Consequently it has been looked for the formation of a chemical bond between the support and the metallocene. A possible solution is the formation of a chemical bond by reacting a functionalized metallocene and a partly dehydrated silica. EP 293815 and DE 3718888 disclose a process for the preparation of a supported catalyst wherein the chemical bond between support and metallocene is obtained by reaction of an alkoxy group bond to silicon and the hydroxy group of the support. The synthesis of this catalyst is difficult and very low yields were obtained. Furthermore the catalytic activity in O-olefin polymerization is quite low.
DE 3840772 discloses the use of metallocenes functionalized by vinyl groups bonded to the cyclopentadienyl ring. The double bond is further reacted with polysiloxanes. This method presents the drawback of the use of an additional catalyst, essential for reacting the double bond with siloxane. This requires a further purification step in order to remove the catalyst.
According to EP 628566 it is possible to prepare heterogeneous catalysts by reacting ligands directly bonded to the cyclopentadienyl ring with alkyllithium and metal halides of formula MX.sub.4 (wherein M is a transition metal and X is halide). This process results in catalysts wherein the metallocene is very tightly bonded to the support. They are used in olefin polymerization in combination with alumoxane. Also in this case the catalyst component needs to be purified in order to remove the residue of the compounds used in the preparation of the catalyst component.
In the present invention a method for obtaining heterogeneous catalyst components is described wherein a properly functionalized metallocene is contacted with an inorganic support.
The present invention also discloses new metallocenes particularly suitable for the preparation of the supported catalyst component of the present invention.
A further object of the present invention is the use of these catalyst components in combination with a cocatalyst for polymerizing O-olefins.
A further object of the present invention is the use of specific compounds for the modification of the inorganic support.
The catalyst components according to the invention present a very strong bond between the metallocene and the support without losing catalytic activity. Furthermore the by-products resulting from the synthesis of the catalyst component do not reduce the catalytic activity and thus do not need to be removed. The so obtained catalyst polymerizes O-olefins in high yields and without phenomena of leaching of the metallocene from the support.